1. Field of the Invention
The present invention relates to improved shift logic for an automated vehicular mechanical transmission system. In particular, the present invention relates to a control method/system having logic rules whereby in the automatic shifting mode, upshifts are initiated normally as a function of throttle position (demand) but, under certain conditions, are initiated as a function of engine torque and not of throttle position (demand).
2. Description of the Prior Art
Fully and partially automated vehicular mechanical transmission systems are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290; 4,850,236; 5,109,721; 5,393,276; 5,409,432 and 5,425,284, the disclosures of which are incorporated herein by reference. Such transmissions having an automatic shift mode typically base shift decisions upon shift point profiles or shift schedules, which often are graphically represented on a graph of throttle position (demand) versus engine, output shaft or vehicle speed. It is known to temporarily modify these shift profiles in view of various sensed vehicle operating conditions to modify vehicle performance, for antihunt purposes or the like. Examples of such shift logic may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,551,802; 4,852,006; 4,916,979; 5,053,963 and 5,406,861, the disclosures of which are incorporated herein by reference.
While the prior art systems which based upshift decisions on demand usually responded to the driver's intent in most situations, a problem not addressed by the prior art shift logic involves systems which will cause engine torque to be significantly restricted, regardless of throttle position, under certain operating conditions. These systems include all-speed governors, road-speed governors (when maximum ground speed is being approached), gear-down protection, etc. When these systems are active to significantly restrict engine torque regardless of a relative high throttle position, basing upshift decisions on demand will delay upshifting, usually in opposition to the driver's intent.